U.S. patent application number 11/719542 was filed with the patent office on 2009-03-12 for heat shrink films and articles encapsulated therein.
Invention is credited to Christopher J. Blackwell, Kevin O. Henderson, Payal Kaul.
Application Number | 20090068486 11/719542 |
Document ID | / |
Family ID | 36127456 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090068486 |
Kind Code |
A1 |
Blackwell; Christopher J. ;
et al. |
March 12, 2009 |
HEAT SHRINK FILMS AND ARTICLES ENCAPSULATED THEREIN
Abstract
The present invention relates to a heat shrink film for
encapsulating articles comprising a core layer having an upper
surface and a lower surface, a first skin layer on the upper
surface of the core layer, and a second skin layer underlying the
lower surface of the core layer, wherein the core layer comprises a
blend of (i) at least one polyterpene and (ii) a syndiotactic
polypropylene or a cyclic olefin copolymer, wherein the ultimate
shrinkage of the film is at least 25% at 135.degree. C.
Inventors: |
Blackwell; Christopher J.;
(Solon, OH) ; Henderson; Kevin O.; (Willoughby
Hills, OH) ; Kaul; Payal; (Beachwood, OH) |
Correspondence
Address: |
RENNER, OTTO, BOISSELLE & SKLAR, LLP (AVERY)
1621 EUCLID AVE, 19TH FL
CLEVELAND
OH
44115-2191
US
|
Family ID: |
36127456 |
Appl. No.: |
11/719542 |
Filed: |
December 22, 2005 |
PCT Filed: |
December 22, 2005 |
PCT NO: |
PCT/US05/46964 |
371 Date: |
May 17, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60638490 |
Dec 23, 2004 |
|
|
|
Current U.S.
Class: |
428/516 ;
428/523 |
Current CPC
Class: |
B32B 2307/542 20130101;
B32B 2307/736 20130101; B32B 2553/00 20130101; B32B 25/18 20130101;
B32B 27/32 20130101; B32B 2439/70 20130101; B32B 2457/10 20130101;
B32B 25/042 20130101; B32B 2250/248 20130101; Y10T 428/31938
20150401; Y10T 428/31913 20150401 |
Class at
Publication: |
428/516 ;
428/523 |
International
Class: |
B32B 27/32 20060101
B32B027/32 |
Claims
1. A multilayered heat shrink film for encapsulating articles
comprising: a core layer having an upper surface and a lower
surface; a first skin layer on the upper surface of the core layer;
and a second skin layer underlying the lower surface of the core
layer; wherein the core layer comprises a blend of (i) at least one
polyterpene; (ii) a syndiotactic polypropylene or a cyclic olefin
copolymer; and (iii) a nucleated homopolymer or copolymer of
polypropylene, wherein the ultimate shrinkage of the film is at
least 25% at 135.degree. C. as measured by ASTM D1204.
2. The film of claim 1 wherein the polyterpene comprises a
hydrogenated polyterpene.
3. The film of claim 1 wherein the core layer further comprises
polyisobutylene.
4. The film of claim 1 wherein the core layer further comprises one
or more thermoplastic polymers.
5. The film of claim 4 wherein the core layer further comprises one
or more of (i) a copolymer of polypropylene and another alpha
olefin, (ii) a copolymer of polyethylene and another alpha olefin,
(iii) a polyethylene, and (iv) combinations thereof.
6. The film of claim 1 wherein the first and second skin layers
comprise one or more polyolefins.
7. The film of claim 6 wherein the one or more polyolefins comprise
one or more of a homopolymer of butylene, a copolymer of
polypropylene and another alpha olefin, a copolymer of polyethylene
and another alpha olefin, a polyethylene, a functionalized
polyethylene, and combinations thereof.
8. The film of claim 7 wherein the first and second skin layers
further comprise a hydrogenated polyterpene.
9. The film of claim 7 wherein at least one skin layer further
comprises a thermoplastic material of a copolymer of an
ethylene-unsaturated carboxylic acid or anhydride, an ionomer
derived from sodium, lithium, or zinc and ethylene/unsaturated
carboxylic acid or anhydride copolymers or combinations
thereof.
10. The film of claim 1 wherein the shrink tension of the film is
less than 3135 kPa at 135.degree. C., as measured by ASTM Method
D2838.
11. A heat shrink film for encapsulating articles comprising a
blend of: (i) a nucleated homopolymer of polypropylene; (ii) at
least one polyterpene; and (iii) a syndiotactic polypropylene or a
cyclic olefin copolymer wherein the ultimate shrinkage of the film
is at least 25% at 135.degree. C. as measured by ASTM Method
D1204.
12. The film of claim 11 wherein the polyterpene is a hydrogenated
polyterpene.
13. The film of claim 11 wherein the film further comprises one or
more thermoplastic polymers.
14. The film of claim 11 wherein the film is uniaxially oriented in
the machine direction only.
15. The film of claim 11 wherein the shrink tension of the film is
less than 3135 kPa at 135.degree. C. as measured by ASTM D2838.
16. The film of claim 11 wherein the film is a monolayer film.
17. The film of claim 11 wherein the film further comprises
polyisobutylene.
18. The film of claim 11 wherein the film comprises a multilayer
film.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/638,490, filed Dec. 23, 2004.
TECHNICAL FIELD OF THE INVENTION
[0002] The invention relates to a heat shrink film having high
shrink and low shrink tension in conjunction with high cross
direction (CD) tensile modulus and high CD bending resistance or
stiffness. More specifically, the invention relates to heat shrink
films which are useful in encapsulating articles, such as
batteries, liquid and powdered food and beverage containers, and
irregular shaped containers that require heat shrinkable packaging
and/or labeling, such as toys and containers.
BACKGROUND OF THE INVENTION
[0003] Shrink films have been used for years to encapsulate
articles. The shrink films must be able to shrink sufficiently to
provide a smooth consistent coating. Previously, shrink films have
been polyolefins and polyolefin blends which were and are used
extensively in the food and packaging business to protect and
preserve articles. Shrink films are also used to label containers.
Initially, labeling operations were carried out using processes and
methods that required the formation of a tube or sleeve of the heat
shrink film which was then placed over the container and heated in
order to shrink the film to conform to the size and shape of the
container.
[0004] More recent packaging processes do not require a preformed
sleeve and permit the application of the film directly from a
continuous roll of film material onto the container. High-speed
continuous operations generally employ biaxially oriented
polypropylene shrink films. Such polypropylene shrink films have
the ability to shrink up to about 25% as tested per ASTM Method D
2732 and ASTM Method D 1204. However, it is often desirable to
obtain shrinkage of anywhere from 15 to 75%.
[0005] Polyvinyl chloride (PVC) films provide acceptable shrinkages
of about 40%. However, such PVC shrink films do not have sufficient
heat stability. After formation of the shrink film, the film should
not shrink prematurely. Often the film is exposed to relatively
high temperatures after formation, such as in transport. It is
desired that the shrink film not shrink until application with heat
to the bottle or article. Another disadvantage of PVC shrink films
is the potential environmental impact of PVC film. Concern over the
adverse affect of halogens on the ozone layer has lead to efforts
to provide halogen free shrink films.
[0006] As an additional consideration, high-speed continuous
operations require the use of an adhesive that will form an
adequate bond between the container and the label. More
specifically, the bond must be such that it will not separate at
the seam during the heat-shrinking step. The bond should also form
a smooth package, which will not bubble or cause creasing of the
film during application. As the level of shrinkage desired is
increased, the adhesive used in the high-speed applications must be
able to provide an adequate bond while maintaining an acceptable
appearance, e.g., without distortion. The adhesive must be
compatible with the particular shrink film material used.
[0007] One problem with polyolefin and polyolefin film blends is
the difficulty of printing on the film. For printing to be
successful, the films must provide a surface which will accept
printing. Additionally, the films must have sufficient tensile
modulus to withstand the rigors of the printing process. Many
polyolefin films do not have the tensile strength to withstand
gravure printing. While orienting of the film uniaxially or
biaxially can increase tensile strength and stiffness of the film
sufficiently to withstand the printing process, conformability of
the film to an article during the shrink process is decreased.
[0008] Appearance and structural defects are also encountered with
shrink films. When shrink films are used for encapsulating
cylindrical articles such as batteries or liquid beverage
containers, the film must shrink sufficiently to encase the
article. A common problem with encapsulating such articles is end
puckering. End puckering occurs when the shrink film does not
shrink sufficiently to provide a smooth encapsulating film at the
ends of the battery. The film folds over itself and forms a
"pucker". This puckering is unacceptable to consumers and the
manufacturer. Further, the shrink film can have fish eye defects
which are small circular bubbles or ridges that can form on the
film due to an apparently localized homogenous shrinking of the
film.
[0009] In addition to "pucker" and "fish eye", high shrink force or
shrink tension in shrink films can lead to film shearing of the
adhesive such that adhesive seams are not flush. This occurs in the
case of low shear strength adhesives at the shrink temperature in
question or when small cross sectional areas of adhesive are
applied relative to the shrink label itself. A partial or complete
adhesive failure can occur if the resulting force of the shrink
film is in excess of the shear strength of the adhesive. In extreme
circumstances, severe pulling and picking of the seams leads to
ripping of the seam apart and failure of the shrink film to shrink
over the desired package. Previously, shrink tension has been
controlled by the use of large amounts of 1-polybutene. Shrink
tension is measured by ASTM Method D2838. This use, however, while
controlling shrink tension, adds cost to the product. It also
adversely effects haze and modulus of the film when combined with
certain polyolefins. This leads to the haze of the film being
higher than desirable, and modulus being too low to process.
[0010] Therefore, it is desirable to have a film, which provides
high shrinkages, e.g., shrinkages of at least 25%, while imparting
a high CD modulus, ultimate CD tensile and bending stiffness. It is
also desired to minimize the shrink force or shrink tension of the
film in applications sensitive to high shrink tension. The desired
film would smoothly encapsulate articles and avoid end puckering
and shearing of adhesive seams.
SUMMARY OF THE INVENTION
[0011] In one aspect, the invention relates to a multilayered heat
shrink film for encapsulating articles comprising a core layer
having an upper surface and a lower surface, a first skin layer on
the upper surface of the core layer, and a second skin layer
underlying the lower surface of the core layer, wherein the core
layer comprises a blend of (i) at least one polyterpene and (ii) a
syndiotactic polypropylene or a cyclic olefin copolymer, wherein
the ultimate shrinkage of the film is at least 25% at 135.degree.
C.
[0012] In another aspect, the invention relates to a heat shrink
film for encapsulating articles comprising a blend of (i) a
homopolymer of polypropylene, (ii) at least one polyterpene; and
(iii) a syndiotactic polypropylene or a cyclic olefin copolymer
wherein the ultimate shrinkage of the film is at least 25% at
135.degree. C.
[0013] In yet another aspect, the invention relates a multilayered
heat shrink film for encapsulating articles comprising a core layer
having an upper surface and a lower surface, a first skin layer
overlying the upper surface of the core layer, a second skin layer
underlying the lower surface of the core layer, wherein the core
layer comprises a blend of a (i) a homopolymer of polypropylene and
(ii) at least one polyterpene and (iii) a syndiotactic
polypropylene or a cyclic olefin copolymer, wherein the ultimate
shrinkage of the film is at least 25% at 135.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic illustration of the side view of a
multilayered film embodying the present invention in a particular
form.
[0015] FIG. 2 is a schematic illustration of the side view of an
embodiment of the multilayered film of the present invention
including a tie layer.
[0016] FIG. 3 is a schematic illustration of the side view of an
embodiment of the multilayered film of the present invention
including sub skin layers.
[0017] FIG. 4 is a diagram of an apparatus for single-stage
stretching for a uniaxially oriented film of the present
invention.
[0018] FIG. 5 is a diagram of an apparatus for two-stage stretching
for a uniaxially oriented film of the present invention.
[0019] FIG. 6 is a plot of the percent shrinkage (dimension change)
versus change in temperature from 20 to 160.degree. Celsius for the
film of the present invention and commercially available films.
[0020] FIG. 7 is a plot of the maximum shrink force (N) versus
change in temperature, from 20 to 1600 Celsius for the film of the
present invention and commercially available films.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention relates to heat shrink films and
labels produced therefrom. The films and labels have a shrinkage of
from about 15% up to about 75% with a low shrink tension desirable
for the specific application use. The shrinkage is determined by
ASTM Method D1204. The films, in one aspect, may be oriented in the
machine direction, e.g., uniaxially oriented. In another aspect,
the film may be biaxially oriented. The film may be a monolayer
film or a multilayer film comprising two or more layers. The film
typically has a thickness from about 0.5 mils to about 12.0 mils.
Here and elsewhere in the specification and claims, the range and
ratio limits may be combined.
[0022] The term "overlies" and cognate terms such as "overlying"
and the like, when referring to the relationship of one or a first
layer relative to another or a second layer, refers to the fact
that the first layer partially or completely overlies the second
layer. The first layer overlying the second layer may or may not be
in contact with the second layer. For example, one or more
additional layers may be positioned between the first layer and the
second layer.
[0023] As used herein, the term "ultimate shrinkage" means the
maximum shrinkage the film is capable of achieving at a particular
shrink temperature, as measured by ASTM Method D 1204. The term
instantaneous shrinkage means the shrinkage obtained when the film
is exposed to the shrink temperature for less than 1 second. The
instantaneous shrinkage of a particular film is determined by
extrapolating the shrinkage percentage obtained for the film using
ASTM Method D 2732 for immersion times of 10, 20, 40, 60, 120 and
240 seconds at a specified shrinkage temperature.
[0024] The films and labels of the present invention are
illustrated in reference to the attached drawings. FIG. 1 is a
schematic illustration of a side view of a film of the present
invention. Film 100 is a coextrudate that comprises core layer 110
which has a first surface 112 and a second surface 114, first skin
layer 120 on the upper surface of the core layer and second skin
layer 130 on the lower surface of the core layer.
[0025] The overall thickness of the film 100 may be in the range of
about 0.5 to about 12.0 mils, and in one embodiment of about 1 mils
to about 8 mils, and in one embodiment of about 1.5 mils to about 4
mils. The thickness of the core layer may range from about 30% to
about 90% of the overall thickness of the multilayered film 100,
and in one embodiment about 40% to about 85%, and in one embodiment
about 50% to about 80% of the overall thickness of the film 100.
The first 120 and second 130 skin layers may have a thickness of
about 5 to about 35% of the overall thickness of the film 100, and
in one embodiment about 10 to about 30%, and in one embodiment
about 15% to about 25% of the overall thickness of the film 100.
The first 120 and second 130 skin layers can be the same thickness
or of a different thickness.
[0026] The shrink tension of the film 100, as measured by ASTM
D2838 at 135.degree. C., in one embodiment is less than 3135 kPa
(kilopascals), and in one embodiment less than 2653 kPa, and in one
embodiment less than 2274 kPa, and in one embodiment less than 2067
kPa.
Core Layer
[0027] The core layer comprises a major portion of the multilayer
shrink film. Typically, the core layer has a thickness from about
0.6 to about 4, or from about 0.8 to about 3, or from about 1 to
about 2.5, or from about 1.2 to about 2 mils thick. The films have
sufficient strength to be printed by flexographic and gravure
printing. These films generally have a Young's modulus from about
60,000 to about 500,000, or from about 100,000 to about 400,000, or
from about 150,000 to about 300,000 psi. Young's modulus is
determined by ASTM D882-61T
[0028] As described above, the multilayered shrink films have, in
one embodiment, a core layer, which may be comprised of a
polypropylene resin and a polyterpene additive in a carrier resin.
The polypropylene generally comprises a polypropylene homopolymer,
a nucleated polypropylene homopolymer, a polypropylene copolymer, a
nucleated polypropylene copolymer, or mixtures thereof. In one
embodiment, the polypropylene resin comprises a nucleated
polypropylene homopolymer. An example of a commercially available
nucleated polypropylene homopolymer that may be used is P4GK-173X
from Huntsman. This material is identified as having a melt flow
rate of 12 g/10 min. (ASTM D1238), a density of 0.9 g/cm.sup.3
(ASTM D1505) and a flexural modulus of 1310 MPa (ASTM D790). Other
examples of commercially available nucleated homopolymers are BP
Amaco homopolymer HF12G1 and Dow H700-12NA.
[0029] The polyterpene resin generally comprises a blend or
concentrate of a polyterpene in a carrier resin, such as a
polypropylene homopolymer or copolymer. The polyterpene resin
blended with the polypropylene resin provides improved stiffening
action, increased modulus and increased strength of the resulting
film, as well as acting as a densifying component that can lower
the shrink force of the film. The polyterpene resins are a
well-known class of resinous materials obtained by the
polymerization or copolymerization of one or more terpene
hydrocarbons such as the alicylic, mono-cyclic and bicyclic
terpenes, and their mixtures, including careen, isomerised pinene,
dipentene, terpinene, terpinolene, turpentine, a terpene cut or
fraction, and various other terpenes.
[0030] In one embodiment, the polyterpene comprises a hydrogenated
polyterpene, which is also effective for improving the properties
of the films. These are produced by hydrogenating the polyterpenes
by any of the usual hydrogenation processes. Generally, the
hydrogenation is carried out utilizing a catalyst such as nickel,
nickel on kieselguhr, copper chromite, palladium on alumina, or
cobalt plus zirconia or kieselguhr. Hydrogenation can be
accomplished in an inert solvent such as methyl cyclohexane,
toluene, p-methane, etc., utilizing pressures ranging from 500 to
10,000 psi and a temperature of 1500 to 300.degree. C. Useful
hydrogenated polyterpenes include those having a melt index of 8-15
g/10 min. at 190.degree. C. An example of a commercially available
hydrogenated polyterpene resin is Exxelor PA609A from Exxon Mobil.
This resin is identified as having a melt index of 11 g/10 min.
(ASTM D1238) and a density of 0.975 g/cm.sup.3 (ASTM D1505).
Another example of a commercially available polyterpene resin is
Exxelor PA609N from Exxon Mobil. This resin is identified as having
a melt index of 11 g/10 min and a density of 0.975 g/cm.sup.3.
[0031] The blend of polypropylene resin and polyterpene resin is
comprised of about 10% to about 60% by weight of polypropylene
resin and about 40% to about 90% polyterpene resin. In one
embodiment, the blend comprises from about 20% to about 40%
polypropylene resin and about 15% to about 40% polyterpene
resin.
[0032] In addition to the polypropylene resin and the polyterpene
resin, the core layer, in one embodiment, will contain syndiotactic
polypropylene blended with the propylene and polyterpene resins.
Syndiotactic polypropylene is a polypropylene having a high
syndiotacticity, such that the syndiotactic index or [r] value
obtained from NMR data is at least 0.7. Such syndiotactic
polypropylene is described in U.S. Pat. Nos. 5,476,914 and
6,184,326, incorporated herein by reference. Commercially available
syndiotactic polypropylene useful in the present invention includes
those available from Atofina under the trade designations Finaplas
1471, Finaplas 1571 and Finaplas 1251. In one embodiment, the core
layer contains syndiotactic polypropylene in an amount from about
20% to about 70% by weight, in another embodiment, about 30% to
about 60% by weight, and in another embodiment about 35% to about
55% based on total weight of the core layer.
[0033] In one embodiment, the core layer will contain one or more
additional thermoplastic polymers. The thermoplastic polymer can
comprise a polyolefin, an alkene-vinyl carboxylate ester copolymer,
an alkene-alkyl (meth)acrylate copolymer, an ethylene-butyl
acrylate or methacrylate copolymer, a grafted or functionalized
polyolefin, an impact polymer, an ionomer, or combinations
thereof.
[0034] In one embodiment, the core layer will contain a copolymer
of propylene with an alpha olefin. The copolymers of propylene
generally have a melt flow of about 0.5 to about 12 g/10 min, or
from about 4 to about 12 g/10 min. The polyolefins which can be
utilized in the core layer 110 include polymers and copolymers of
olefin monomers containing from about 2 to about 12 carbon atoms,
or from about 2 to about 8 carbon atoms, such as ethylene,
propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, etc.
Preferred alpha olefins are ethylene and 1-butene or blends of
mixtures of such polymers and copolymers. In one embodiment the
polyolefins comprise polymers and copolymers of ethylene and
propylene. In another embodiment, the polyolefins comprise
copolymers such as propylene-ethylene and propylene-1-butene
copolymers. Blends of polypropylene and polyethylene with each
other, or blends of either or both of them with
polypropylene-polyethylene copolymer also are useful.
[0035] In addition to the nucleated polypropylene homopolymer resin
and polyterpene resin, the core layer may also contain other film
forming polymeric resins in a lesser amount, generally about 5 to
about 45% by weight based on the total weight of the core layer. In
one embodiment, the core layer contains about 20 to about 40% by
weight, and in another embodiment, about 20% to about 35% by weight
of a polymeric resin based on the total weight of the core layer.
Such polymeric resins include copolymers of ethylene with another
alpha olefin, functionalized polyethylene, low density
polyethylene, a copolymer of ethylene and propylene, cyclic olefin
copolymer, or a mixture of two or more thereof. The copolymers of
ethylene with another alpha olefin include ethyl vinyl acetate
copolymers (EVA), ethylene butyl acrylate copolymer (EBA), ethylene
methyl acrylate (EMA), functionalized or grafted polyethylenes, and
polyethylenes with a hexene or octene branch, such as Dow Affinity
KC 8852. A useful EVA copolymer is AT Plastics 1821A. An example of
a useful EMA is TC-120 from Exxon Mobil, and an EBA being Eastman
Kodak's SP 1802. Useful functionalized or grafted polyethylenes
include DuPont Bynel 3048, an anhydride modified ethylene vinyl
acetate, DuPont Bynel 3101, an acid/acrylate modified ethylene
vinyl acetate, DuPont Bynel 4006, an anhydride modified high
density polyethylene, and DuPont Bynel 41E556, an anhydride
modified linear low density polyethylene. The polyethylenes
utilized will generally be high density polyethylene, linear low
density and very low-density polyethylenes. A useful high density
polyethylene is HD2015 from Huntsman. Examples of useful linear low
density polyethylenes (LLDPE) are L8148 available from Huntsman,
Dynex.RTM. D6053C, MarFlex.RTM. PE7109L and Vytek.RTM. V208C6, all
available from Chevron Phillips. Commercially available very
low-density polyethylenes (VLDPE) or metallocene polyethylenes
include Dow Affinity KC 8852, Dow Attane 4402, Nova Sclair 10A, and
Exxon Exact 4151. Useful ethylene-propylene copolymers include
P5M4K-070X available from Huntsman, Acclear 8359 from BP Amaco, and
Versify 3000, Versify 3200 and Versify 3300 available from Dow
Chemical. Useful cyclic olefin copolymers include Ticona Topaz 8007
and Topaz 9506. Other cyclic olefins can be found from Zeon
Chemicals LP as Zeonor 1020R and Zeonor 1060R.
[0036] In one embodiment, a homopolymer of butylene or a copolymer
of butylenes with an alpha olefin is blended with the propylene
copolymer described above. The copolymer of butylene with an alpha
olefin may comprise a copolymer of butylene with ethylene,
propylene, butylene, pentene, hexane, heptene, octane, nonene,
decene, etc. Particularly useful are butylene-ethylene copolymers.
The butylene-ethylene copolymer typically includes ethylene at a
level of about 0.5% to about 12%. Examples of useful
butylene-ethylene copolymers are those available from Basell under
the trade designation DP 8220, which has an ethylene content of 2%
and a melt flow of 2.0 g/10 min, and under the trade designation DP
8310, which has an ethylene content of 6% and a melt flow of 3.2
g/10 min. Examples of butylene homopolymers include those
identified as 0300 (melt flow 4.0 g/10 min) available from Basell.
The copolymer of butylenes may also comprise an
ethylene-propylene-butylene terpolymer.
[0037] The core layer, in one embodiment, includes polyisobutylene
(PIB), which has been found to lower the crystallinity of isotactic
polypropylene and, in specific combinations with other olefins,
lower the shrink tension, while reducing fish eye defects in the
film. The polyisobutylene may be selected from one or more low
molecular weight polyisobutylenes having a viscosity average
molecular weight of from 36,000 to 70,000. Such polyisobutylenes
are commercially available under the trademark Vistanex from Exxon
Chemical as grades LMMS, LMMH and LMH, having viscosity average
molecular weights of about 45,000, 53,000 and 63,000 respectively.
The low molecular weight polyisobutylene may be present in an
amount corresponding to from about 0.2% to about 5.5% by weight of
the core layer. High molecular weight polyisobutylene may be used
in the viscosity average molecular weight range of 800,000 to
2,500,000 and is exemplified by the Vistanex MM series of products,
available from Exxon Chemical. The polyisobutylene generally
comprises, in one embodiment, from about 0.2% to about 5.5%, and in
one embodiment from about 0.5% to about 4%, and in one embodiment
from about 1% to about 3%.
[0038] Table 1 contains examples of formulations for the core layer
of the present films. Here and throughout the specification and
claims the amounts are by weight, unless clearly indicated
otherwise.
EXAMPLES
TABLE-US-00001 [0039] TABLE 1 PEH Core or Identity SPP.sup.1
NPPH.sup.2 PIB.sup.3 PT.sup.4 PPC.sup.5 PEC.sup.6 PB.sup.7
COC.sup.8 C1 40 20 0.5 39.5 -- -- -- -- C2 50 30 3 17 -- -- -- --
C3 46.5 29 2.5 22 -- -- -- -- C4 40 40 -- 20 -- -- -- -- C5 60 5 1
20 5 9 -- -- C6 40 20 1 9 10 5 15 -- C7 40 -- 1 30 -- 29 -- -- C7A
40 -- 1 30 29 -- -- -- C8 40 -- 1 29 30 -- -- -- C9 30 10 -- 20 20
20 -- -- C10 35 -- -- 50 -- 15 -- -- C11 70 -- -- 20 -- 10 -- --
C12 -- 20 -- 20 -- 20 -- 40 C13 -- 20 -- 20 -- 40 -- 20 .sup.1SPP
is syndiotactic polypropylene. .sup.2NPPH is nucleated
polypropylene homopolymer. .sup.3PIB is polyisobutylene. .sup.4PT
is polyterpene. .sup.5PPC is polypropylene copolymer. .sup.6PEH or
PEC is polyethylene homopolymer or polyethylene copolymer. .sup.7PB
is poly(1-butene). .sup.8COC is cyclic olefin copolymer.
Skin Layer
[0040] The multilayer shrink film can comprise one or more skin
layers. The skin layers can be printable skin layers. In one
embodiment, the film 100 has a first skin layer 120 on the upper
surface 112 of the core layer 110 and second skin layer 130 on the
lower surface 114 of the core layer 110. In one embodiment, skin
layers 120, 130 comprise the same composition. In another
embodiment, skin layers 120, 130 are different in composition. In
one embodiment, skin layers 1230, 130 comprise a thermoplastic
polymer or copolymer derived from propylene or ethylene. The
homopolymers and copolymers of propylene and ethylene are described
above.
[0041] In one embodiment, skin layers include one or more of the
above-described alpha olefins such as polyethylene, polybutylene,
an ethylene-butylene copolymer, or an ethylene-propylene-butylene
terpolymer; an ethylene-methyl acrylate copolymer; an
ethylene-vinyl acetate copolymer; an ethylene-ethyl acrylate
copolymer; a poly(methyl methacrylate), an
acrylonitrile-butadiene-styrene copolymer; a nylon; a polybutene; a
polyisobutylene; a polystyrene; a polyurethane; a polysulfone; a
poly(vinylidene chloride); a polycarbonate; a
poly(4-methyl-1-pentene), a styerne-maleic anhydride copolymer; a
styrene-acrylonitrile copolymer; a cellulosic, a fluoroplastic, a
polyacrylonitrile; a thermoplastic polyester, or mixtures thereof.
The polyolefin blend is typically present in an amount from about
20% up to about 100% in one embodiment, and from about 40% to about
99% in one embodiment, and from about 30% up to about 70% by weight
in one embodiment.
[0042] In another embodiment, the multilayer film of the present
invention comprises at least one skin layer comprising a
thermoplastic material of a copolymer of an ethylene-unsaturated
carboxylic acid or anhydride, an ionomer derived from sodium,
lithium or zinc and ethylene/unsaturated carboxylic acid or
anhydride copolymers or combinations thereof. Useful ionomer resins
include those available from DuPont under the tradename Surlyn.
These resins are identified as being derived from sodium, lithium
or zinc and copolymers of ethylene and methacrylic acid, including
Surlyn 1605, 7940 and 9120. Ethylene-methacrylic acid copolymers
that are useful include those available from DuPont under the
tradename Nucrel, such as include Nucrel 0407, which has a
methacrylic acid content of 4% by weight and a melting point of
109.degree. C. Useful ethylene/acrylic acid copolymers include
those available from Dow Chemical under the tradename Primacor,
such as Primacor 1430, which has an acrylic acid monomer content of
9.5% by weight and a melting point of 97.degree. C. The
concentration of the foregoing thermoplastic polymers in the skin
layer 120 is generally from about 20% to about 100%, based on the
overall weight of the skin layer 120, and in one embodiment from
about 30% to about 50%.
[0043] In one embodiment, at least one of the skin layers comprises
a homopolymer of butylene. Examples of butylenes homopolymers
include those identified above available from Basell. The butylenes
generally comprises from about 5 to about 35% in one embodiment,
and in one embodiment from about 15% to about 20% based on the
total weight of the skin layer.
[0044] In another embodiment at least one of the skin layers will
comprise a polyterpene as described above. In one embodiment the
skin layer will comprise from about 10% to about 90% polyterpene,
and from about 30% to about 70% polyterpene in another
embodiment.
[0045] Table 2 illustrates examples of formulations for the skin
layers:
TABLE-US-00002 TABLE 2 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 Nucleated 60
0 20 50 0 0 0 90 50 60 Homopolymer PP PP-alpha olefin 0 60 30 0 80
100 0 0 50 0 Copolymer PE or PE-alpha 40 40 50 50 0 0 100 0 0 40
olefin copolymer Ionomer 0 0 0 0 20 0 0 10 0 0 Polybutene-1 0 0 0 0
0 0 0 0 0 0 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 Nucleated 0 20
60 40 70 80 0 100 35 100 Homopolymer PP PP-alpha olefin 60 30 40 60
20 10 80 0 35 0 Copolymer PE or PE-alpha 40 50 0 0 10 0 0 0 20 0
olefin copolymer Ionomer 0 0 0 0 0 0 0 0 5 0 Polybutene-1 0 0 0 0 0
10 20 0 5 0 S21 S22 S23 S24 S25 S26 S27 S28 S29 S30 Nucleated 95 0
0 20 0 20 70 30 0 25 Homopolymer PP PP-alpha olefin 0 70 50 30 0 20
0 50 40 25 Copolymer PE or PE-alpha 5 30 0 10 40 20 30 0 0 10
olefin copolymer Ionomer 0 0 0 0 0 10 0 0 0 0 Polybutene-1 0 0 0 0
0 0 0 0 0 5 Polyterpines 0 0 50 40 60 30 0 20 60 25
[0046] In one embodiment, it is desired to subject the surface of
at least one of the skin layers to a high-energy discharge (or
plasma) such as the high-energy electrical discharges produced by
corona discharge and glow discharge which are well-known in the
industry. Corona discharge is a high-energy, high-ionizing
discharge that is produced at electrodes when a high voltage is
applied across the plates of a condenser (capacitor). The corona
discharge treatment improves the surface energy of the upper
surface of the skin layer and improves printability of the surface.
Alternatively, the surface of at least one skin layer is subjected
to variations of corona treatment such as covered roll, universal
roll (also known as dual dielectric) and bare roll technologies. In
another embodiment, flame treatment is used to treat the skin
layer. The skin layers may be printed using conventional printing
techniques. For example, gravure, flexographic and UV flexographic
printing processes may be used to print the skin layer. Water
based, solvent based and UV curable inks may be used to print the
skin layer. In one embodiment, the film is reverse printed with a
design, image or text so that the print side of the skin is in
direct contact with the surface to which the film is applied.
[0047] As noted above, the core layer is relatively thick compared
to the outer, e.g., skin layers. Thus, the core layer may be bout 2
to 20 times as thick as each of the outer layers. Examples of
thickness ratios of the core to the outer layers combined include
90:10, 80:20, 70:30 etc. The thickness ratios of the skin layer to
the core and then to the other skin layer are 1-20:60-90:1-20, or
5-15:70-90:5-15. Thickness ratios of three layered films include
5:90:5, 10:80:10, 15:70:15, 20:60:20, etc. The two skin layers do
not have to be of equal thickness.
[0048] The skin layers 120 and 130 may contain an effective amount
of a processing aid to facilitate extrusion. While not wishing to
be bound by theory, it is believed that these processing aids have
a high affinity to metal surfaces and thereby prevent or reduce the
tendency of the polymer compositions being extruded from adhering
to the inner walls of the extrusion equipment. This makes it easier
to purge the extrusion equipment during color changeovers. These
processing aids include hexafluorocarbon polymers. An example of a
commercially available processing aid that can be used is Ampacet
401198 which is a product of Ampacet Corporation identified as a
hexafluoro carbon polymer. The processing aids are typically used
at concentrations of up to about 1.0% by weight, and in one
embodiment about 0.2% to about 0.5% by weight.
[0049] The film 110 may contain pigments, fillers, stabilizers,
optical brighteners, anti-oxidants, glow in the dark concentrates,
nucleating agents, clarifying agents, process aids, oxygen
scavengers, anti-fog agents, foaming agents, light protective
agents or other suitable modifying agents if desired. Pigments or
color concentrates may be used to add color, such as white, black,
gray, blue, red, orange, yellow, or green. Examples of useful
pigments are: Ampacet 101359-B (white Ti02 concentrate), Ampacet
150425 (red concentrate), Ampacet 13381-A (yellow concentrate),
Ampacet 12083 (silver concentrate), Ampacet 17106 (green
concentrate), Ampacet 14445 (orange concentrate), Ampacet 161201
(blue concentrate), and Ampacet 190405 (black concentrate). An
example of a useful optical brighter is Ampacet 40247. An example
of a useful UV light stabilizer is Ampacet 10561. A useful
antioxidant is Polyfil 0524M. Useful nucleating agents include
Miliken's Milad 3988 and Amfine's NA11 and NA21.
[0050] The film may also contain anti-block, slip additives and
anti-static agents. Useful anti-block agents include inorganic
particles, such as clays, talc, calcium carbonate and glass. An
example of a useful antiblock is Ampacet 401960 (Seablock-4). A
synthetic silica antiblock from A. Schulman that is useful is
ABPP05-SC. Slip additives useful in the present invention include
polysiloxanes, waxes, fatty amides, fatty acids, metal soaps and
particulate such as silica, synthetic amorphous silica and
polytetrafluoroethylene powder. A useful slip additive is SPER 6
from A. Schulman. Other slip additives from Ampacet include 10025,
100329, and 100358-XL. Anti-static agents useful in the present
invention include alkali metal sulfonates, polyether-modified
polydiorganosiloxanes, polyalkylphenylsiloxanes and tertiary
amines. A useful antistatic agent is VLA55SF from A. Schulman.
Other useful anti-static agents from Ampacet include 10053 and
101710.
[0051] In one embodiment, the film 100 has a low coefficient of
friction (COF) surface, which can allow movement of the film while
it is being shrink onto an article. Lack of movement can cause
defects such as wrinkles, air pockets and fish eyes. In one
embodiment, a low COF surface comprises a slip agent such as an
erucamide or oleamide which is incorporated into the film or a skin
layer. In one embodiment, a low COF surface comprises an inherently
low COF polymer such as a high density polyolefin in the film or a
skin layer.
[0052] In one embodiment, as shown in FIG. 2, the multilayer shrink
film 100 of the present invention may comprise one or more tie
layers 140, 150. Tie layer 140, 150 may be any polymer which
improves adhesion of the layers. Examples of suitable tie layers
include: polyethylene copolymers including those having a high
alpha-olefin content, ethylene methacrylic acid copolymers, ethyl
vinyl acetate copolymers, anhydride grafted ethyl vinyl acetate
copolymers, anhydride grafted ethylene polymers, ionomers, styrene
butadiene copolymers, and C.sub.3 or higher polyolefin copolymers
having a high alpha olefin comonomer contents such as a
propylene-1-butene copolymer having a 1-butene content up to 14% by
weight.
[0053] In another embodiment, the film 100 can include one or more
subskin layers 160, 170 between the skin layers 120, 130 and tie
layers 140, 150, as shown in FIG. 3. The subskin layers may be
comprised of the same materials as the skin layer 120 and/or skin
layer 130.
[0054] The heat shrink films may be prepared by means known to
those in the art. The film may be prepared by co-extrusion through
a cast-die or annular die, extrusion coating through a cast die or
annular die, a coating, or a lamination. In one embodiment, the
shrink film is a lamination of two separate multilayer films. In
another embodiment, the film is a lamination of a multilayer film
and a monolayer film, or combinations thereof. In one embodiment,
the film is made through a cast process in which the film is made
in roll form, followed by stretching in a machine direction
orientation line. In one embodiment, the film is made via a blown
film or bubble process followed by stretching as described above.
In another embodiment, the film is made via a double bubble process
and the two films laminated together.
[0055] The films can be of equal or different thicknesses and of
the same or different compositions. In one embodiment, the
lamination is an adhesive lamination using a pressure sensitive
adhesive. In another embodiment, the lamination is a heat seal
lamination.
[0056] The films may also be taken through secondary processes.
This includes metallization through vacuum metallization; printable
topcoats applied as needed to enhance the decorative nature of the
label, lamination, or protective coatings such as lacquers.
[0057] As discussed above, the films may be directionally oriented.
In one embodiment, the films will be uniaxially oriented.
Uniaxially oriented films are stretched in only one direction.
Machine direction orientation is accomplished by stretching the
film as is known in the art. In one embodiment, the extruded sheet
is stretched in the machine direction only, in a single-stage
stretching process. FIG. 4 illustrates an apparatus 10 useful for
the single-stage stretching of the film of the present invention.
The extruded film proceeds through preheat rolls 1 and 2, and then
draw rolls 3 and 4 where it is stretched. The film then passes
through annealing rolls 5 and 6, and then to cooling rolls 7 and 8.
In one embodiment of the single stage stretching process, preheat
rolls 1 and 2 are set at 220.degree. F. (104.degree. C.), draw
rolls 3 and 4 are set at 230.degree. F. (110.degree. C.), annealing
rolls 5 and 6 are set at 150.degree. F. (66.degree. C.), and
cooling rolls 7 and 8 are set at 100.degree. F. (38.degree. C.) and
75.degree. F. (24.degree. C.). The draw ratio between rolls 3 and 4
is about 5.5:1. In generally, the multilayer films of the present
invention typically have a stretch ratio from about 2 to about 9,
or from about 3.5 to about 7, or from about 4 to about 6. In
general, the temperature ranges of the preheat rolls are from about
180.degree. F. (82.degree. C.) to about 260.degree. F. (127.degree.
C.), the draw rolls from about 180.degree. F. (82.degree. C.) to
about 260.degree. F. (127.degree. C.), the annealing rolls from
about 100.degree. F. (38.degree. C.) to about 260.degree. F.
(127.degree. C.) to, and the cooling rolls from about 75.degree. F.
(24.degree. C.) to about 130.degree. F. (54.degree. C.).
[0058] In another embodiment, the extruded sheet is uniaxially
oriented using a two-stage stretching process wherein the extruded
sheet is stretched twice in the machine direction. FIG. 5
illustrates an apparatus 20 useful for two-stage stretching of the
film of the present invention. The extruded film proceeds through
preheat rolls 21 and 22, and then draw rolls 23 and 24 where it is
stretched. The film then passes through another set of preheat
rolls 25 and 26, and then a second set of draw rolls 27 and 28
where it is again stretched. The film then passes through annealing
rolls 29 and 30, and then to cooling rolls 31 and 32. In one
embodiment of the two-stage stretching process, preheat rolls 21
and 22 are set at 230.degree. F. (110.degree. C.), draw rolls 23
and 24 are set at 245.degree. F. (118.degree. C.), preheat roll 25
is set at 260.degree. F. (127.degree. C.), preheat roll 26 and draw
rolls 27 and 28 are set at 200.degree. F. (93.degree. C.),
annealing rolls 29 and 30 are set at 150.degree. F. (66.degree. C.)
and cooling rolls 31 and 32 are set at 100.degree. F. (38.degree.
C.) and 75.degree. F. (24.degree. C.), respectively. The draw ratio
between draw rolls 23 and 24 is about 4.5 to 1, and between draw
rolls 27 and 28 is about 1.2-1.5:1.
[0059] As described above, the films are useful in many shrink film
applications for encapsulating articles including batteries,
aluminum soda can containers, aerosol cans, plastic liquid beverage
containers, plastic milk containers, powdered containers such as
powdered coffee creamer or powdered lemonade, glass containers
holding food and beverage product, and irregular shaped containers
that require heat shrinkable packaging such as toys, health and
beauty aids, pharmaceutical/nutritional applications such as:
vitamins, powered nutritional supplements, baby formula, cosmetics
such as foundation and lipstick, lip balm, and hand soaps and
sanitizers in plastic containers. In one embodiment of a labeling
process, a roll of the film is fed into a label applicator where a
transport feed roller directs the film to a cutting station. At the
cutting station, a cutting drum shear cuts the film into segments.
The film segment, or label, is directed to the adhesive station
where an adhesive strip is applied to both the leading edge and
trailing edge of the label. A vacuum assisted drum then transfers
the label to the article to be labeled. A UV lamp cures the
adhesive on the leading and trailing edges of the label. The
article with the affixed label is then sent through a heat shrink
tunnel where the label shrinks to conform to the article. These
tunnels can be hot air, steam or IR heated. The label application
process is a high-speed process.
[0060] Useful adhesives for such applications include adhesives
that are capable of shrinking with the shrink film, at least 40%,
and in one embodiment up to 80%, without adversely affecting the
appearance of the film or becoming detached from the article. Such
adhesives include hot melt adhesives and radiation curable
adhesives. A particularly useful radiation curable adhesive
comprises:
[0061] (a) a base resin, such as an epoxidized block copolymer (as
described in U.S. Pat. No. 5,516,824 and U.S. Pat. No. 5,776,998);
and/or a cycloaliphatic epoxy (such as CYRACURE UVI6110 available
from Dow Chemical); an olefin including that having a C--C double
bond pendant to the backbone or on ends--such materials may be
oligomeric, polymeric or monomeric and the backbone may vary in
polarity ranging from aliphatic, urethane, polyester and
polyether);
[0062] (b) a photoinitiator, the type of which is dependent on the
type of chemistry of the base resin, e.g., cationic photoinitiator
suitable for curing epoxidized block copolymer, cycloaliphatic
epoxies, and vinyl ether olefins which includes sulfonium or
iodonium salts such as SARCAT CD1010, SARCAT CD1011 and SARCAT
CD1012 (available from Sartomer) and CYRACURE UVI 6974 available
from Dow Chemical. For free-radical curing systems such as olefinic
or thiol-ene curing systems the following photoinitiators may be
suitable: IRGACURE 651, 184 and 1700 and DAROCURE 1173, available
from CIBA-GEIGY; as well as GENOCURE LBP available from Rahn; and
ESACURE KIP150 available from Sartomer. Other examples of
photoinitiators which may be used include one or more of the
following: benzophenone, benzyldimethyl ketal,
isopropyl-thioxanthone,
bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl) phosphineoxide,
2-hydroxy-2-methyl-1-phenyl-1-propanone,
diphenyl(2,4,6-trimethybenzoyl) phosphine oxides,
1-hydroxycyclohexyl phenyl ketone,
2-benzyl-2-(dimethyl-amino)-1-4-(4-morpholinyl)phenyl-1-butanone,
alpha,alpha-dimethoxy-alpha-phenylacetophenone,
2,2-diethoxyacetophenone,
2-methyl-1-4-(methylthio)phenyl-2-(4-morpholinyl)-1-propanone,
2-hydroxy-1-4-(hydroxyethoxy)phenyl-2-methyl-1-propanone.
[0063] (c) a tackifier, such as the C.sub.5-C.sub.9 hydrocarbon
resins, synthetic polyterpenes, rosin, rosin esters, natural
terpenes, and the like. More particularly, the useful tackifying
resins include any compatible resins or mixtures thereof such as
natural and modified rosins including gum rosin, wood rosin, tall
oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin,
and polymerized rosin; glycerol and pentaerythritol esters of
natural and modified rosins, including the glycerol ester of pale,
wood rosin, the glycerol ester of hydrogenated rosin, the glycerol
ester of polymerized rosin, the pentaerythritol ester of
hydrogenated rosin, and the phenolic-modified petaerythritol ester
of rosin; copolymers and terpolymers of natural terpenes, such as
styrene/terpene and alpha methyl styrene/terpene; polyterpene
rosins generally resulting from the polymerization of terpene
hydrocarbons, such as the bicyclic monoterpene known as pinene, in
the presence of Friedal-Crafts catalysts at moderately low
temperatures; also included are the hydrogenated polyterpenes
resins; phenolic modified terpene resins and hydrogenated
derivatives thereof such as, for example, the resin product
resulting from the condensation, in an acidic medium, of a bicyclic
terpene and a phenol; aliphatic petroleum hydrocarbon resins
resulting from the polymerization of monomers consisting primarily
of olefins and diolefins; hydrogenated aliphatic petroleum
hydrocarbon resins; and cyclic or acyclic C.sub.5 resins and
aromatic modified acyclic or cyclic resins. Mixtures of two or more
of the above-described tackifying resins may be required. An
example of a commercially available solid hydrogenated tackifer is
ESCOREZ 5400 from Exxon. Examples of useful liquid tackifying
resins include REGALITE R-10 a C.sub.5 liquid tackifier with a
softening point of 10.degree. C. available from Hercules, and
WINGTACK 10, a liquid hydrocarbon resin with a softening point of
10.degree. C. available from Goodyear Chemical Co.;
[0064] (d) a diluent, such as a plasticizing or extending oil
including olefin oligomers and low molecular weight polymers as
well as vegetable and animal oil and their derivatives. The
petroleum derived oils which may be employed are relatively high
boiling materials containing only a minor proportion of aromatic
hydrocarbons (preferably less than 30% and, more particularly, less
than 15% by weight of the oil). Alternatively, the oil may be
totally non-aromatic. Suitable oligomers include polypropylenes,
polybutenes, hydrogenated polyisoprene, hydrogenated polybutadiene,
or the like having average molecular weights between about 350 and
about 10,000. Examples of useful mineral oils include refined
hydrocarbon oils such paraffinic, aromatic and naphthalenic oils
available under the trade designations KAYDOL from Witco, TUFFLO
from Arco, and the like;
[0065] (e) a wax, such as a petroleum derived paraffinic or
mycrocrystalline wax (including PACEMAKER 53 available from Citgo)
is useful for altering the viscosity, green strength, and reducing
tack of the final composition;
[0066] (f) a compatible polymer such as a block copolymer including
polystyrene-polybutadiene-polystyrene,
polystyrene-polyisoprene-polystyrene,
poly(alpha-methyl-styrene)-polybutadiene-poly(alpha-methyl-styrene),
poly(alpha-methyl-styrene)-polyisoprene-poly(alpha-methylstyrene),
as well as the hydrogenated modifications thereof, e.g.,
polystyrene-poly(ethylene-butylene)-polystyrene. These copolymers
may be prepared by methods taught, for example, in U.S. Pat. Nos.
3,239,478; 3,247,269; 3,700,633; 3,753,936 and 3,932,327. For
higher polarity systems, polymers such as polyesters (e.g. DYNAPOL
materials available from Huls and sulfonated polyesters (available
from Eastman under the AQ series) and acrylic polymers (such as
ACRONAL AC205 and ACRONAL AC 258 available from BASF) which are
also reactive with free-radical systems and non-reactive acrylics
(such as those available from Schenectady Chemical). Other,
non-limiting examples of additional materials include the
following: SBR random copolymers with low (<20%) or high
(>20%) vinyl contents, available under the trade name DURADENE
from Firestone (these high vinyl copolymers are reactive and
contribute to the crosslinking of the system); EPDM copolymers
which can react into the polymer network via unsaturated sites, and
saturated analogs (e.g. EP rubber) that can modify the peel and
tack of the adhesive. These are available from Exxon under the
trade name VISTALON; butyl rubber, which is a copolymer of isoprene
and isobutylene and is available from Exxon Chemical under the
trade name VISTANEX; and liquid polyisopropylene such as is
available from Kuraray, Inc. under the trade name LIR;
[0067] (g) an alcohol-containing co-reactant for cationic curing
systems which is often added to adjust crosslink density, Tg,
viscosity and specific adhesion. Examples include, polyester
polyols available from Stepan Chemical Company and from Dow
Chemical; polyalkylene oxide polyols such as PEG and PPG available
from Dow Chemical; aliphatic diols such as L-2203 available from
Shell (this is an ethylene butylene diol); and L-1203 an ethylene
butylene mono-ol available from Shell; also useful are
polybutadiene polyols available from Atochem; epoxidized
polybutadiene polyols for alcohols may also be used; and
[0068] (h) other additives known to those skilled in the art. These
additives may include, but are not limited to, pigments, fillers,
fluorescent additives, flow and leveling additives, wetting agents,
surfactants, antifoaming agents, rheology modifiers, stabilizers,
and antioxidants. Preferred additives are those that do not have
appreciable absorption in the wavelengths of interest.
[0069] In one embodiment, the radiation curable adhesive comprises
(a) from about 5% by weight to about 60% by weight of at least one
epoxidized block copolymer; (b) from about 20% by weight to about
85% by weight of at least one solid-hydrogenated tackifier; (c)
about 0.02% by weight to about 5% by weight of at least one
cationic photoinitiator; (d) about 0% by weight to about 40% by
weight of at least one mineral oil; (e) about 0% by weight to about
40% by weight of at least one liquid tackifier; and (f) about 0% by
weight to about 3% by weight of an antioxidant.
[0070] In another embodiment, the radiation curable adhesive
comprises (a) from about 10% by weight to about 50% by weight of at
least one epoxidized cycloaliphatic base resin; (b) about 0.1% by
weight to about 2.0% by weight of at least one cationic
photoinitiator; (c) about 0% by weight to about 80% by weight of at
least one solid or liquid polyester diol; and (d) about 0% by
weight to about 60% by weight of at least one polar tackifier. Such
radiation curable adhesives are described in European Patent
Application, EP 1130070.
[0071] A particularly useful radiation curable adhesive is
Contour.TM. adhesive available from National Starch.
[0072] The adhesive is used to affix the heat shrink labels to the
article or container using conventional packaging equipment.
Examples of packaging equipment and label applicators are disclosed
in U.S. Pat. Nos. 4,749,428; 4,844,760; 4,923,557; 5,512,120;
5,855,710; 5,858,168 and 5,964,974, incorporated by reference
herein. The adhesive may be applied to a portion of the outer
surface of at least one of the skin layers by any known method. For
example, the adhesive may be applied by spraying, dipping, rolling,
gravure or flexographic techniques.
[0073] Alternatively, the adhesive may be applied directly to the
article or container to be labeled. The label is then applied to
the article and subjected to heat to shrink the label onto the
container so as to affix the label to container.
[0074] In one embodiment, the film is laminated to a pressure
sensitive adhesive with liner. The film is die cut to form
individual labels and the matrix surrounding the labels are
removed. The resulting labels are then applied to a battery and
shrink wrapped in a heat tunnel. The temperature of the heat tunnel
is approximately 250-260.degree. F. The labels may further include
circuitry such as that used to determine the strength of the
battery charge.
[0075] Table 3 contains examples of multilayered films of the
present invention. These films are prepared by coextrusion and are
uniaxially oriented to a stretch ratio of 5.5:1 to provide a film
with a 2 mil gauge.
TABLE-US-00003 TABLE 3 Film 1 Film 2 Film 3 Film 4 Film 5 Film 6
Film 7 Skin S2 S2 S2 S22 S2 S2 S2 layer Core C1 C2 C3 C4 C5 C7 C8
Layer Skin S10 S10 S10 S10 S10 S10 S10 Layer
[0076] The coextruded films of Table 3 had the properties listed
below in Table 4.
TABLE-US-00004 TABLE 4 Property Film 1 Film 2 Film 3 Film 4 Film 5
Film 6 Film 7 MD Oil.sup.a 36.6 39.6 37.3 25.7 34.1 41.3 40.6
Shrink, % MD Oven.sup.b 43.4 41 43.3 33.5 37.3 50.4 51.6 Shrink, %
MD Shrink 296 386 324 450 313 190 298 Tension.sup.c, psi MD
Modulus.sup.d, 257,000 269,000 205,000 274,000 210,000 134,000
233,000 Psi CD Modulus.sup.d, 135,000 164,000 117,000 142,000
129,000 97,000 104,000 Psi MD L&W.sup.e, 21.5 22.5 22.5 28.9
23.6 18.6 17.9 mN CD L&W.sup.e, 9.5 9.5 10.5 16 10.8 8.5 9.2 mN
Haze, % 8.7 9.4 8.5 6.1 8.7 9.9 10.5 .sup.aInstantaneous shrinkage
135.degree. C. oil per ASTM Method D2732. .sup.bUltimate shrinkage
in 135.degree. C. oven per ASTM Method D1204. .sup.cShrink tension
per ASTM Method D2838. .sup.dTensile modulus per ASTM Method D882.
.sup.eBending resistance in millinewtons via L&W apparatus.
[0077] Table 5 provides a comparison of maximum shrink tension and
force for inventive films of Samples 2 and 3 (respectively, XRFS
and 1030-178-1 which correspond to Film 1 of Table 3 prepared on a
pilot line coextruder and a production line coextruder) versus a
commercial oriented polystyrene film (Fasson OPS), a commercial
biaxially oriented polypropylene film (Mobil Roso), and an oriented
polyolefin film of Sample 1 (EFD-A) containing a core layer of
syndiotactice polypropylene and polypropylene copolymer.
TABLE-US-00005 TABLE 5 Shrink Shrink Sample Tension L .times. W
.times. T (mm) Force Fasson OPS 55 Spec #77018: 545 psi 9.973 5.860
0.050 1.100 Sample 1: 427 psi 9.997 6.130 0.050 0.9032 Sample 2
(inventive): 386 psi 9.996 5.930 0.050 0.7895 Mobil Roso
polypropylene: 381 psi 10.047 5.960 0.030 0.4629 Sample 3
(inventive): 335 psi 10.040 5.920 0.060 0.8198
[0078] FIG. 6 depicts the % shrinkage or dimension change for the
five films of Table 5 using a constant force of 0.005N versus
change in temperature, from 20 to 160.degree. Celsius.
[0079] FIG. 7 depicts the shrink force in Newtons (N) for the films
of Table 5 with change in temperature, from 20 to 180.degree.
Celsius from which a maximum shrink force and tension was obtained
for Table 5.
[0080] The shrink films of the present invention have high %
shrinkage and equivalent or lower shrink force or tension as
compared to the commercially available known films.
[0081] While the invention has been explained in relation to
specific embodiments, it is to be understood that various
modifications thereof will become apparent to those skilled in the
art upon reading the specification. Therefore, it is to be
understood that the invention disclosed herein is intended to cover
such modifications as fall within the scope of the appended
claims.
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